1. Field of the Invention
The present invention relates generally to multi-stage mechanical mechanisms for the initiation of pyrotechnic materials in thermal batteries or the like devices requiring pyrotechnic initiation in munitions, and more particularly for initiation of such pyrotechnic materials in munitions following a predetermined number of deceleration events such as the so-called set-forward acceleration in gun-fired munitions and mortars or target impact events. The means of the said activation may be mechanical by causing certain relevant motion in the system/device to be produced or electrical by causing a circuit to be closed or opened and/or electrical pulses to be generated or cause other detectable events that indicate the impact event and/or the severity of the impact.
2. Prior Art
Thermal batteries represent a class of reserve batteries that operate at high temperatures. Unlike liquid reserve batteries, in thermal batteries the electrolyte is already in the cells and therefore does not require a distribution mechanism such as spinning. The electrolyte is dry, solid and non-conductive, thereby leaving the battery in a non-operational and inert condition. These batteries incorporate pyrotechnic heat sources to melt the electrolyte just prior to use in order to make them electrically conductive and thereby making the battery active. The most common internal pyrotechnic is a blend of Fe and KClO4. Thermal batteries utilize a molten salt to serve as the electrolyte upon activation. The electrolytes are usually mixtures of alkali-halide salts and are used with the Li(Si)/FeS2 or Li(Si)/CoS2 couples. Some batteries also employ anodes of Li(Al) in place of the Li(Si) anodes. Insulation and internal heat sinks are used to maintain the electrolyte in its molten and conductive condition during the time of use. Reserve batteries are inactive and inert when manufactured and become active and begin to produce power only when they are activated.
Thermal batteries have long been used in munitions and other similar applications to provide a relatively large amount of power during a relatively short period of time, mainly during the munitions flight. Thermal batteries have high power density and can provide a large amount of power as long as the electrolyte of the thermal battery stays liquid, thereby conductive. The batteries are encased in a hermetically-sealed metal container that is usually cylindrical in shape. Thermal batteries, however, have the advantage of very long shelf life of up to 20 years that is required for munitions applications.
Thermal batteries generally use some type of igniter to provide a controlled pyrotechnic reaction to produce output gas, flame or hot particles to ignite the heating elements of the thermal battery. There are currently two distinct classes of igniters that are available for use in thermal batteries. The first class of igniter operates based on electrical energy. Such electrical igniters, however, require electrical energy, thereby requiring an onboard battery or other power sources with related shelf life and/or complexity and volume requirements to operate and initiate the thermal battery. The second class of igniters, commonly called “inertial igniters”, operates based on the firing acceleration. The inertial igniters do not require onboard batteries for their operation and are thereby often used in high-G munitions applications such as in gun-fired munitions and mortars.
In general, the inertial igniters, particularly those that are designed to operate at relatively low impact levels, have to be provided with the means for distinguishing events such as accidental drops or explosions in their vicinity from the firing acceleration levels above which they are designed to be activated. This means that safety in terms of prevention of accidental ignition is one of the main concerns in inertial igniters.
In an activated thermal battery, since the electrolyte is in its molten state, the battery cannot withstand high-G shocks that are caused as the munitions impacts a hard surface such as the intended target. For this reason, when the thermal battery is intended to be used to power certain devices following target impact, then it is highly desirable for the thermal battery to be activated following such shock loadings. In certain applications, the munitions is intended to enter the interior of a building or a bunker through more than a single wall, ceiling, floor or otherwise significant barrier (hereinafter, all such significant barriers are referred to collectively as “significant barriers”, with the aim of including those obstacles that cause shock loading of the munitions above certain predetermined level and excluding minor obstacles that are not used for protection against incoming munitions). In such applications, it is highly desirable for the thermal battery to be initiated following a prescribed number of shock loadings (impacts), each corresponding to shock loading due to impact with a significant barrier.
It is appreciated by those skilled in the art that an initiation device that is used to ignited pyrotechnic materials in thermal batteries may also be used to initiate pyrotechnics materials in other devices or initiate explosive charges.